Hi theaomai, thanks for the question!
There’s a misconception that sunscreen needs to “bind” with your skin cells in order to activate protection. This is a myth for both physical (inorganic) and chemical (organic) sunscreens.
The chemicals themselves absorb the UV wavelengths, not the skin cells – what’s important is that the sunscreen is able to form an even layer on the skin.
Too much oil on the skin, could prevent a sunscreen from forming an even layer, just by virtue of being greasy and by preventing the sunscreen from drying or applying smoothly. Same goes with wet skin.
If you can still move the sunscreen on the skin after you’ve applied it, that means over time gravity will pull more sunscreen into the crevices of your skin – making the sunscreen coverage uneven. Not to mention it’ll be more easily wiped off!
I would recommend gently blotting any excess oil off the skin before applying your sunscreen.
Hope that helps!